Galactic synchrotron distribution derived from 152 HII region absorption features in the full GLEAM survey

TL;DR

This study maps the Milky Way's synchrotron emission by analyzing HII region absorption features across multiple frequencies, introducing a new emissivity calculation method that enhances understanding of Galactic magnetic fields and cosmic-ray electrons.

Contribution

A novel method for calculating synchrotron emissivity using HII region absorption, providing detailed Galactic distribution insights and extending to the Sun.

Findings

Derived synchrotron emissivity to the Galactic edge and Sun.

Improved method for emissivity calculation using Haslam map and spectral indices.

Mapped Galactic magnetic field and cosmic-ray electron distribution.

Abstract

We derive the synchrotron distribution in the Milky Way disk from HII region absorption observations over -40{\deg} < l < 40{\deg} at six frequencies of 76.2, 83.8, 91.5, 99.2, 106.9, and 114.6 MHz with the GaLactic and Extragalactic All-sky Murchison widefield array survey (GLEAM). We develop a new method of emissivity calculation by taking advantage of the Haslam et al., (1981) map and known spectral indices, which enable us to simultaneously derive the emissivity and the optical depth of HII regions at each frequency. We show our derived synchrotron emissivities based on 152 absorption features of HII regions using both the method previously adopted in the literature and our improved method. We derive the synchrotron emissivity from HII regions to the Galactic edge along the line of sight and, for the first time, derive the emissivity from HII regions to the Sun. These results provide direct information on the distribution of the Galactic magnetic field and cosmic-ray electrons for future modelling.